Grease composition and machine elements

ABSTRACT

A grease composition which contains a large amount of thickener, and may prevent a flaking effectively for a long period of time, and machine elements in which the grease composition is filled are provided. A grease composition comprising a thickener and a base oil, characterized in that the thickener contains a diurea compound represented by the Formula (I): 
       R 1 —NHCONH—R 2 —NHCONH—R 3 ,  (I)         wherein R 1  and R 3  are a phenyl group and/or a cyclohexyl group, R 2  is a C 6 -C 15  divalent hydrocarbon group, and the molar ratio of cyclohexyl group/(cyclohexyl group+phenyl group) in R 1  and R 3  is 0.95 to 0.10.

TECHNICAL FIELD

The present invention relates to a grease composition and machine elements, and particularly, to a grease composition which is suitably used for rolling bearings and constant-velocity joints for automobile instruments or auxiliaries, and to a rolling bearing, or constant-velocity joints in which the grease composition is filled.

BACKGROUND ART

The service life of lubrication units used for rolling and rolling-sliding is associated with fatigue, i.e. flaking. In order to prevent this flaking and prolong the service life, it is required to decrease the frequency of direct contact of both surfaces lubricating with each other. As a method of not contacting both the surfaces each other, a measure is generally taken to increase the viscosity of the lubricating oil, i.e. the base oil in the grease, and to thicken the oil layer.

However, some amount of thickener is needed in order for this effect to be demonstrated. On the other hand, when the amount of the thickener is too high, the property of the grease composition to easily flow into a lubricating unit is impaired, and therefore, a countermeasure thereto is required.

Such a property of the grease composition is strongly required when machine elements to be lubricated are constant-velocity joints, gears or rolling bearings for automobiles.

As greases used for rolling bearings for automobile instruments or auxiliaries, a diurea grease in which the base oil mainly comprises a synthetic hydrocarbon oil and a phenyl ether synthetic oil is used. Among diurea greases, particularly aromatic diurea is often used because of its high temperature resistance.

However, this kind of grease lacks the property to easily flow into the lubricating unit and thus generates a flaking due to insufficiency of lubricant.

On the other hand, as an example of providing the inflow property by a thickener,

Patent Document 1 proposes a grease characterized in that a gelling agent is incorporated as an essential ingredient in a base oil comprising more than 50% by weight of ether synthetic oil, which gelling agent comprises at least one of diurea compounds represented by the following general formula,

R²—NHCONH—R¹—NHCONH—R³,

wherein R¹ represents a C₆-C₁₅ divalent aromatic hydrocarbon group, R² and R³ are the same or different groups and each of R² and R³ represents a cyclohexyl group, a C₇-C₁₂ cyclohexyl derivative group or a C₈-C₂₀ alkyl group, and in which gelling agent, the content ratio of cyclohexyl group or derivative group thereof [{(cyclohexyl group or derivative group thereof)/(cyclohexyl group or derivative group thereof+alkyl group)×100} is 50 to 100%. However, with this grease, the thickener is short and needs improvement in the flaking.

Patent Document 1 JP 2979274 B

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a grease composition which contains a large amount of a thickener and which prevents flaking effectively for a long period and which has an excellent inflow property, and machine elements in which the grease is filled.

Another object of the present invention is to provide a grease composition which, if used for machine elements such as constant-velocity joints, gears, rolling bearing and the like, has an improved property to easily flow into the lubrication unit and has a long fatigue life even under high temperature conditions, and machine elements in which the grease is filled.

Means for Solving the Problems

The present invention provides the grease composition described below and machine elements using the grease composition.

1. A grease composition comprising a thickener and a base oil, characterized in that the thickener contains a diurea compound represented by the Formula (I),

R¹—NHCONH—R²—NHCONH—R³,  (I)

wherein R¹ and R³ are a phenyl group and/or a cyclohexyl group, R² is a C₆-C₁₅ divalent hydrocarbon group, and the molar ratio of cyclohexyl group/(cyclohexyl group+phenyl group) in R¹ and R³ is 0.95 to 0.10.

2. The grease composition according to the above-described item 1, wherein the base oil comprises a mineral oil. 3. The grease composition according to the above-described item 1, wherein the base oil comprises a phenyl ether based synthetic oil. 4. The grease composition according to any one of the above-described items 1 to 3, which is for rolling lubrication units and/or rolling-sliding lubrication units. 5. The grease composition according to any one of the above-described items 1 to 4, which is for constant velocity joints and/or gears for automobiles. 6. The grease composition according to any one of the above-described items 1 to 4, which is for rolling bearings. 7. A machine element in which the grease composition according to any one of the above-described items 1 to 4 is filled. 8. The machine element according to the above-described item 7, which is a constant velocity joint and/or a gear for automobiles. 9. The machine element according to the above-described item 7, which is a rolling bearing.

EFFECTS OF THE INVENTION

Because the grease composition of the present invention contains a sufficient amount of thickener and the inflow property of the grease composition into the lubrication unit is improved, the fatigue life of machine elements such as constant-velocity joint, gear and bearing is long.

The grease composition of the present invention may be generally applied to rolling bearing. Particularly, the grease composition of the present invention may suitably be used for rolling bearings for automobile instruments or auxiliaries which rolling bearings have flaking problems. Such bearings include electromagnetic clutches for automobile air conditioners; bearings used for intermediate pulley, idler pulley and tension pulley and bearings used for alternators.

Further, the grease composition of the present invention is suitably used for constant velocity joints such as fixed-type (e.g., Rzeppa-type and Barfield-type) constant-velocity joints; and slide-type (e.g., double offset type and cross groove type) constant-velocity joints.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Generally, in a rolling lubrication system or a rolling-sliding lubrication system, a 1 flaking is associated with the service life, which needs improvement. The present invention was completed based on the finding that a grease composition which uses a specific diurea thickener may effectively prevent the direct contact between both the surfaces lubricating each other, and improves anti-flaking property without increasing the viscosity of the base oil. The grease composition of the present invention comprising a specific diurea compound as a thickener easily enters between the lubricating surfaces of rolling to prevent the direct contact of both the surfaces of the metals and to effectively prevent a flaking.

The base oil used for the present invention is not restricted and those usually used for grease compositions may be employed. A base oil having a kinematic viscosity of 10 to 400 mm²/s, more preferably 20 to 250 mm²/s, and still more preferably 40 to 150 mm²/s at a temperature of 40° C. is preferred.

Examples of the base oil include mineral oils, synthetic oils and natural oils. Examples of the synthetic oils include hydrocarbon oils, aromatic oils, ester oils and ether oils. Examples of the hydrocarbon oils include poly-α-olefins such as normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, 1-decene and ethylene co-oligomer and hydrogenation products thereof. Examples of the aromatic oils include alkyl benzenes such as monoalkyl benzenes and dialkyl benzenes and alkyl naphthalenes such as monoalkyl naphthalenes, dialkyl naphthalenes and polyalkyl naphthalenes. Examples of the ester oils include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate and ditridecyl glutarate; aromatic ester oils such as trimellitic acid esters, pyromellitic acid esters; polyol ester oils such as trimethylolpropane esters, pentaerythritol esters and dipentaerythritol esters; and complex ester oils which are oligoesters of polyhydric alcohols and fatty acid mixtures of dibasic acid monobasic acid. Examples of the ether oils include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol mono-ethers and polypropylene glycol mono-ethers; and phenyl ether oils such as monoalkyl triphenyl ethers, alkyl diphenyl ethers, pentaphenyl ether, tetraphenyl ether, monoalkyl tetraphenyl ethers and dialkyl tetraphenyl ethers. Examples of other synthetic oils include tricresyl phosphate, silicone oils and perfluoro alkyl ethers. Examples of the natural oils include fats and oils such as beef tallow, lard, soybean oil, rape oil, rice bran oil, coconut oil, palm oil, palm kernel oil and hydrogenation products thereof. These base oils may be used individually or as a mixture of two or more of them.

Mineral oils and alkyl diphenyl ethers are particularly preferred.

The thickener used for the grease composition of the present invention is a diurea compound represented by the above-described formula (I). R¹ and R³ are a phenyl group and/or a cyclohexyl group, and the molar ratio of cyclohexyl group/(cyclohexyl group+phenyl group) in R¹ and R³ is 0.95 to 0.10, and preferably 0.90 to 0.15.

In the formula (I), R² is a C₆-C₁₅ divalent hydrocarbon group such as a linear or branched alkylene group, a linear or branched alkenylene group, a cycloalkylene group or an aromatic group.

The diurea thickener used in the present invention may be obtained by, for example, reacting a prescribed diisocyanate and a prescribed monoamine. Preferred specific examples of the diisocyante include diphenylmethane-4,4′-diisocyanate (MDI) and tolylene diisocyanate (TDI).

As the monoamine, a mixture of aniline and cyclohexylamine is used in a prescribed ratio. A mixture of a diurea obtained from a diisocyanate and aniline, and a diurea obtained from a diisocyanate and cyclohexylamine, containing the diureas at the above-described prescribed ratio may also be used.

The content of the thickener in the grease composition of the present invention may be the amount which is appropriate for obtaining the required consistency, and the content is usually preferably 1 to 20%, more preferably 2 to 20% by mass based on the total mass of the grease composition.

The grease composition of the present invention may contain additives such as extreme pressure additives, antioxidants, rust preventives and anticorrosives, which are usually used for grease compositions.

EXAMPLES

The present invention will now be described specifically by way of the following examples.

A diurea compound was prepared by reacting diphenylmethane-4,4′-diisocyanate with aniline and/or cyclohexylamine in a prescribed ratio in a base oil. Then the base oil was added to the diurea compound in an amount to attain a consistency of 300 to prepare a test grease composition.

The base oils used are the following two kinds.

Mineral oil: 500 neutral oil (kinematic viscosity at 40° C.: 100 mm²/s) Alkyl diphenyl ether oil: MORESCO HILUBE LB 100 (Matsumura Oil Research Corp.; kinematic viscosity at 40° C.: 100 mm²/s)

The fatigue life test of the grease composition was estimated by the following rolling four ball test.

Outline of Rolling Four Ball Test Method

Three bearing steel balls having a diameter of 15 mm are provided and placed into a cylindrical container having an inside diameter at the bottom of 36.0 mm, an inside diameter at the top end of 31.63 mm and a depth of 10.95 mm, and then 20 g of a test grease is applied. On the tops of these three steel balls, a steel ball for bearing having a diameter of ⅝ inches is contacted and when the steel ball is rotated at a prescribed rotation rate, the bottom three steel balls revolve while rotating. These steel balls are allowed to rotate continuously until a flaking occurs on the surface of the steel ball.

A flaking occurs between balls where the contact pressure is the highest.

The fatigue life is defined as a total rotation number at the time when a flaking occurs.

Test Condition

Test steel ball: (Φ⅝ inch steel ball for bearing (rotating ball), (Φ15 mm steel ball for bearing (driven ball)

Test load (W): 400 kgf (6.5 Gpa)*

Rotation rate (n): 1500 rpm

Number of repeated tests: 5 (average life: average of five tests)

Maximum Herzian pressure between balls. The value of 6.5 Gpa represents a very high contact pressure and a state where the oil film is considerably thin is resulted.

The compositions of the grease compositions and the test results are show in Table 1 and Table 2.

TABLE 1 Examples 1 2 3 4 5 R¹, R³ phenyl 100 90 50 15 0 molar ratio cyclohexyl 0 10 50 85 100 amount of thickener 22 18 16 12 10 (% by mass) base oil mineral oil consistency 300 fatigue life (×1000) 200 3000 5500 4200 1800

TABLE 2 Examples 6 7 8 9 10 R¹, R³ phenyl 100 90 50 15 0 molar ratio cyclohexyl 0 10 50 85 100 amount of thickener 22 18 16 12 10 (% by mass) base oil alkyl diphenyl ether oil consistency 300 fatigue life (× 1000) 350 4200 6100 4800 2200

With the grease compositions (Example 1 and Example 6) where 100% of R¹ and R³ are phenyl groups in the formula (I), since the amount of the thickener was too high for the grease composition to sufficiently flow into the lubrication unit, a flaking occurred early to reach a fatigue life. On the other hand, with the grease compositions (Example 5 and Example 10) where 100% of R¹ and R³ are cyclohexyl groups in the formula (I), since the content of diurea compound was too small, a satisfactory fatigue life was not obtained.

In contrast, with the grease compositions of Examples 2-4 and Examples 7-9 where the molar ratio of cyclohexyl group/(cyclohexyl group+phenyl group) in R¹ and R³ is 0.95 to 0.10 in the formula (I), the time for a flaking to occur was extremely long, and which is therefore effective for preventing occurrence of a flaking in CVJs, gears, rolling bearings and the like.

These results show that the grease composition of the present invention is effective for preventing all the flaking events such as subsurface-initiated flaking and surface-initiated flaking. 

1. A grease composition comprising a thickener and a base oil, characterized in that the thickener contains a diurea compound represented by the Formula (I): R1-NHCONH—R2-NHCONH—R3,  (I) wherein R1 and R3 are a phenyl group and/or a cyclohexyl group, R2 is a C6-C15 divalent hydrocarbon group, and the molar ratio of cyclohexyl group/(cyclohexyl group+phenyl group) in R1 and R3 is 0.95 to 0.10.
 2. The grease composition according to claim 1, wherein the base oil comprises a mineral oil.
 3. The grease composition according to claim 1, wherein the base oil comprises a phenyl ether based synthetic oil.
 4. The grease composition according to claim 1, which is for rolling lubrication units and/or rolling-sliding lubrication units.
 5. The grease composition according to claim 1, which is for constant velocity joints and/or gears for automobiles.
 6. The grease composition according to claim 1, which is for rolling bearings.
 7. A machine element in which the grease composition according to claim 1 is filled.
 8. The machine element according to claim 7, which is a constant velocity joint and/or a gear for automobiles.
 9. The machine element according to claim 7, which is a rolling bearing. 